System Overview
WARNING: This page is about a different car, the 2018 Nissan Titan XD. However, it is still accessible from the selected car via links, so may be relevant.
WARNING:
The fuel system (fuel pump, high pressure fuel lines, fuel rail, injectors) contain very high pressure fuel. To avoid the risk of personal injury or fire:
- Do not loosen any fittings while the engine is running.
- Wait at least 10 minutes after shutting down the engine before loosening any fittings in the high-pressure fuel system to allow pressure to decrease to a lower level.
- Wear appropriate eye protection and protective equipment as high-pressure fuel spray can penetrate skin.
- Never smoke or allow sparks or flames (such as pilot lights, electrical switches, or welding equipment) in the work area. Never allow diesel fuel to spill onto a hot exhaust manifold which can cause a fire.
CAUTION:
To avoid possible engine and system damage or performance issues:
- Brush away all dirt and debris from the area prior to opening any fuel, air intake, exhaust, cooling, aftertreatment or other engine system.
- To avoid contamination, any open engine system ports must be closed immediately with clean care caps or an appropriate covering.
- Do not allow any debris to fall into the engine.
- Do not allow any chemical cleaners to enter the engine or any open systems during the cleaning process.
- The fuel system is a high-pressure common rail electronically controlled fuel system. The high-pressure common rail system consists of three main components:
(1)
: Fuel pump
(2)
: Fuel rail
(3)
: Fuel injector
- The fuel pump supplies high-pressure fuel to the fuel rail (bank 1) then to the fuel rail (bank 2). The volumetric fuel flow from the pump is electronically controlled by the fuel pump actuator. The fuel rails pressure is controlled by an interaction between the fuel rail pressure relief valve and the fuel pump actuator. From the fuel rail, a constant supply of high-pressure fuel is supplied to the fuel injectors. The ECM controls the fueling and timing of the engine by actuating the piezo injectors.
- Cleanliness is extremely important in regard to the fuel system components, due to the precision tolerances of these components.
- Make sure to complete the following:
- Clean all fuel system fittings, lines, and components before disassembly.
- Make sure no dirt or debris enters the fuel system components to prevent the passing of contaminants to the high-pressure fuel rail and fuel injectors.
- Do not pre-fill the Stage 1 or Stage 2 fuel filters.
- Even small amounts of dirt and debris can cause a malfunction of the fuel system components.
Fuel Pump
- The fuel pump (1) is chain driven by the crankshaft.
- The fuel pump consists of two main components:
- Pumping chambers - uses two pistons to build high fuel pressure (200, 000 kPa [2, 040 kg/cm 2 , 29, 000 psi]).
- Fuel pump actuator (2) - used to control the volumetric flow into the pumping chamber.
Fuel Pump Actuator
- The fuel pump actuator (1) is mounted on the fuel pump (2) at the inlet to the pumping chambers. It regulates the volume of fuel that is allowed to enter the pumping chambers. The fuel pump actuator is controlled by the signal from the ECM to maintain the pressure in the fuel rails at a desired level (works in conjunction with the fuel pressure relief valve).
(A)
: Bolts
Fuel Pressure Relief Valve
- The fuel rail pressure relief valve (1) is mounted on the rear side of the fuel rail (bank 2). It is electronically controlled by a signal from the ECM. When no current is applied to the fuel rail pressure relief valve, the valve is open. The fuel rail pressure relief valve and fuel pump actuator work together to maintain the pressure in the fuel rail that is desired. When the fuel rail pressure relief valve is open, fuel flows through the fuel rail pressure relief valve drain line and joins the return flow from the fuel pump back to the Stage 1 fuel filter/ fuel tank.
- The engine uses an electric motor-driven lift pump (1). It is located inside the stage 1 fuel filter housing (2). The lift pump draws fuel from the fuel tank and increases fuel pressure before delivering the fuel to the pump. The electric lift pump operates at a constant speed while the engine is operating. If power is lost to the electric lift pump, the engine will not be able to operate.
Fuel Flow Description
Fuel Supply, Fuel Filter and Fuel Pump
- Fuel is drawn from the fuel supply tank through a suction-side fuel/water separating filter (Stage 1), which is remotely mounted on the vehicle chassis, by the electric lift pump (the suction-side fuel filter, fuel water separator, and electric lift pump are all one assembly). The electric lift pump pressurizes the fuel to approximately 450 - 700 kPa (4.5 - 7 kg/cm 2 , 65.3 - 101.5 psi) absolute. Fuel exiting the electric lift pump is routed to the pressure-side fuel filter (Stage 2), which is mounted on-engine. From the pressure-side fuel filter, fuel flows to the high-pressure fuel pump. The fuel that enters the high-pressure fuel pump is pressurized to between 25, 000 - 200, 000 kPa (255 - 2, 040 kg/cm 2 , 3, 625 - 29, 000 psi) by two pumping chambers.
Fuel Pump Actuator
- A fuel pump actuator mounted on the fuel pump at the inlet to the two pumping chambers regulates the volume of fuel that is allowed to enter the pumping chambers. The fuel pump actuator is controlled by a pulse-width modulation (PWM) signal from the ECM to maintain the pressure in the fuel rail at a desired level. By regulating the volume of fuel that enters the pumping chambers, the pressure delivered by the fuel pump can be controlled.
Cascade Overflow Valve
- Fuel that is not allowed to enter the two pumping chambers is directed through the cascade overflow valve. The cascade overflow valve directs a certain amount of pressurized fuel to the lube channels of the high-pressure fuel pump. The fuel is then routed to the fuel pump drain line, which returns the fuel to the drain manifold at the bottom of the Stage 2 fuel filter, which then combines with the fuel rail pressure relief valve flow and returns to the Stage 1 fuel filter/ fuel supply tank.
Fuel Rail (bank 1) and (bank 2), Fuel Rail Pressure Sensor and Fuel Rail Pressure Relief Valve
- High-pressure fuel leaves the fuel pump through a fuel rail supply line to the fuel rail (bank 1). The fuel rail (bank 1) acts as a fuel manifold, accumulating and distributing fuel to each of the injector supply lines. A fuel rail to fuel rail supply line directs fuel from the fuel rail (bank 1) to the fuel rail (bank 2). The fuel rail (bank 1) contains a fuel rail pressure sensor that monitors the pressure provided to the fuel rails from the fuel pump. Pressure measured by the fuel rail pressure sensor is used by the ECM to adjust the valve positions of the fuel pump actuator and the fuel rail pressure relief valve to maintain desired rail pressure. The fuel rail (bank 2) contains a fuel rail pressure relief valve. The fuel rail pressure relief valve is controlled by a PWM signal from the ECM to maintain the pressure in the fuel rail at a desired level. Fuel from the fuel rail pressure relief valve is routed to the return manifold in the bottom of the Stage 2 fuel filter, and is then routed to the Stage 1 fuel filter/ fuel supply tank.
Injector Supply Lines, Fuel Injectors and Injector Drain Line
- From the injector supply lines, high-pressure fuel is directed to the fuel injectors. Each fuel injector is equipped with a piezo stack that, when commanded by the ECM, controls when the fuel injector provides fuel. Excess fuel not used by the fuel injectors is drained into the injector drain line. The injector drain line returns fuel from both banks of fuel injectors. The return fuel flows through a constant pressure valve and back into the supply fuel in the Stage 2 fuel filter housing. The constant pressure valve keeps constant back-pressure on the injectors at 1100 - 1400 kPa (11.22 - 14.28 kg/cm 2 , 159.5 - 203.1 psi).